The present invention relates to a holder means for the partial thermal treatment in an oven, especially a vacuum chamber oven that provides compressed gas quenching, of workpieces, especially drill bits, that have a working portion and a portion that is to be clamped.
U.S. Pat. No. 5,052,923, Peter et al, discloses a receiving means for tools that are to be subjected to a thermal treatment, with the receiving means being provided with a radiation shield on that side that faces the oven chamber. With this heretofore known holder means, a base plate is provided and has holes for receiving the tools; that side of the base plate that faces the oven chamber is provided with an insulating plate that is intended to prevent thermal conduction to the base plate. As an additional layer, a radiation shield is disposed upon the insulating plate and has a low thermal emission value, i.e., it reflects thermal radiation. Although this known receiving means makes it possible to insulate the base plate from the thermal radiation in the oven chamber, unfortunately the tools have a large transition zone between the hardened working portion and the non-hardened portion that is to be clamped, with this being brought about due to the fact that an insulating plate that is to provide an adequate insulating effect must be very thick. In addition, with the known receiving means the working portion of the tool that is to be hardened exhibits a varying hardness gradient because as a consequence of the radiation shield, which has a high thermal reflection value, the thermal radiation from the surface of the radiation shield is reflected onto the tools and thereby causes the tools to be heated in an irregular manner.
It is therefore an object of the present invention to provide a holder means for the partial thermal treatment of tools or other workpieces in ovens, with such a holder means making it possible to have as small a transition zone on the workpiece as possible and while maintaining a good thermal insulation adequately guiding the workpieces in the base plate.